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Holley 6919: One Idle Mixture Screw Has No Effect

Mikey

Bronco Guru
Joined
Aug 15, 2001
Messages
1,477
I started having a bit of trouble again with my Holley. I can understand if both idle mixture screws have no effect on manifold vacuum....too much transfer slot being exposed, etc. But only one side having no effect? I removed the screw and shot carb cleaner until it came out the idle bleed and it helped the overall carb running but still no affect on that one mixture screw. Manifold vacuum is 17-18" remember the emissions 6919 has fixed fuel metering for idle and the screws control the air...it's backwards from most Holleys....even the screws are different.

I will say that at idle it smells a bit rich to me.....makes me think the metering block may be a bit warped.....seen that before.

Two thoughts:
1). Swap out the metering block.

2). Perhaps the idle circuit of the emissions 6919 isn't rich enough for a 302 with an aluminum intake (85 Mustang GT), Hooker Comp headers and dual exhaust?

Thoughts? Recommendations?
Thanks,
Mike
 

Broncobowsher

Total hack
Joined
Jun 4, 2002
Messages
34,821
I just dealt with this on a Carter/Edelbrock. Just shooting carb cleaner didn't fix it. Had to completely take it apart and chase out every passage. Lets just say I discovered that the bottom of the fuel bowls were in need of a scotchbrite pad and a screwdriver that no can of carb/brake clean was going to touch. Runs good now.
 
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Mikey

Bronco Guru
Joined
Aug 15, 2001
Messages
1,477
What did you use to chase out the tiny passages? I've always used carb spray in my rebuilds with success but I do recall that this rebuild had some pretty gummed up stuff inside. I'm looking at swapping out the metering block....I have another 6919 carb with a bad one anyway.....haven't decided yet....wanting to see ideas.
 

Broncobowsher

Total hack
Joined
Jun 4, 2002
Messages
34,821
Carb cleaner and compressed air. In both directions. Nice thing about a symmetrical carb, if the passages on both sides breath the same, they will work the same. Since there is one good side, that is the reference.
 

B RON CO

Contributor
Bronco Guru
Joined
Jun 29, 2016
Messages
2,411
Loc.
Statesville, NC
Hi, Gunk has a 1 gallon can of carb cleaner with a basket so you can really soak the parts. After the bath I use hot water and then compressed air.
Not every carb needs it, but sometimes nothing else works. Good luck
 
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Mikey

Bronco Guru
Joined
Aug 15, 2001
Messages
1,477
I always hated when people never say what the fix ended up being. So, after trying multiple rebuilds, swapping in another spare rebuilt 6919, swapping metering blocks, etc...I finally bought a used Holley 670cfm Truck Avenger. I only had time to make one run with this new carb after swapping out power valve for a 65, primary jets to 65 and secondaries to 73, it ran like a scalded rabbit and idle vacuum is a solid 20. Hopefully it will stay that way. The Holley sits on an 84 Mustang GT aluminum intake with an Edelbrock 1-inch spacer designed to block off the EGR passage and exhaust dumps into Hooker Comp mid-length headers and dual 2-1/4" pipes. C4 trans.
 

DirtDonk

Contributor
Bronco Guru
Joined
Nov 3, 2003
Messages
47,275
Lot of work, but great that it's fixed!
(well, for now at least...%) )

I've had multiple Holley's that did that, and could only "fix" them temporarily it seemed.
Seems like some tiny bit of junk just finds it's way into just the wrong spot and won't be dislodged if it doesn't feel like it. Maybe?

Thanks for the follow-up. Glad you got it running like it should.

Paul
 

Rustytruck

Bronco Guru
Joined
Feb 24, 2002
Messages
10,875
one of the biggest problems now is once the modern fuels gel up and crystallize there are few cleaners out there that will remove the stuff and takes physical action to remove it. Of the cleaners that will remove it are so caustic it removes the plating making the problem worse down the road.
 

WheelHorse

Bronco Guru
Joined
Nov 22, 2004
Messages
2,491
Glad to hear your truck avenger is working well for you. Most would have just gone to fitech or sniper swearing off carbs all together.
 
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Mikey

Bronco Guru
Joined
Aug 15, 2001
Messages
1,477
Owning 8 cars with all but three having fuel injection, I kinda like tinkering with carbs. So I have two Holleys and one Autolite 4100. Been messing with Holleys for nearly 40 years...EGAD!!!!
 
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